For example, a prober is widely used as an inspecting unit for a semiconductor wafer (which will be hereinafter simply referred to as a “wafer”) in an inspecting process for a semiconductor device. A typical prober comprises a loader chamber and a prober chamber for inspecting electric characteristics of a device in a wafer state. The loader chamber comprises: a cassette mounting portion for mounting thereon a cassette which houses therein a plurality of (e.g., twenty five) wafers; a wafer transfer mechanism for transferring one wafer at a time from the cassette mounting portion; and a pre-alignment mechanism (which will be hereinafter referred to as a “sub-chuck”) for pre-aligning the wafer which is transferred by means of the wafer transfer mechanism. The prober chamber comprises: a supporting table (which will be hereinafter referred to as a “main chuck”) for mounting thereon the wafer to move in X, Y, Z and θdirections; an alignment mechanism which is associated with the main chuck for aligning the wafer; a probe card which is arranged above the main chuck; and a test head which is provided between the probe card and a tester.
Therefore, when an operator intends to inspect a wafer, the operator first mounts a cassette, which houses therein a plurality of wafers every lot, on the cassette mounting portion. Then, when the prober is driven, the wafer transfer mechanism takes one wafer at a time out of the cassette, and the sub-chuck carries out pre-alignment. Thereafter, the wafer transfer mechanism delivers the wafer to the main chuck in the prober chamber. In the prober chamber, the main chuck and the alignment mechanism are associated with each other for pre-aligning the wafer. While the aligned wafer is index-fed by means of the main chuck, the wafer electrically contacts the probe card to inspect predetermined electric characteristics. If the inspection of the wafer is completed, the wafer transfer mechanism in the loader chamber receives the wafer on the main chuck to return the wafer to the original place in the cassette, and thereafter, the inspection of the next wafer is repeated by the above described procedure. If the inspection of all wafers in the cassette is completed, the operator exchanges the wafer for the next wafer to repeat the above described inspection for the new wafer.
However, if wafers have a large diameter of, e.g., 300 mm, the cassette housing therein a plurality of wafers is very heavy, so that it is next to impossible for an operator to carry the cassette. Even if the operator can carry the cassette, there is a risk when the operator carries the cassette alone since it is heavy. In addition, since the particle control in a clean room is increasingly severe with the scale down of semiconductor devices, it is increasingly important to automate manufacturing facilities for cassette transfer and so forth in view of particle control in a clean room. This can be generally applied to semiconductor producing units in addition to probers.
Moreover, there is a jump in the number of devices formed on a single wafer with the increase in diameter of wafers and with the scale down of wafers, and it takes a lot of time to complete processing, such as inspection, with respect to one wafer. In addition, if wafers are processed every lot, processed wafers remain in the prober until the processing of all of the wafers is completed. Therefore, the time required to transfer the wafers of each lot to the subsequent step is delayed. As a result, there is a problem in that it is difficult to shorten TAT (Turn-Around-Time), so that it is difficult to flexibly operate the prober.
Conventionally, there is know an automatic guided vehicle system for transferring each cassette to a large number of processing units, which are provided along a transfer path, by means of an automatic guided vehicle supporting thereon a transfer unit for transferring a cassette which is provided with a large number of shelves for supporting thereon semiconductor wafers. Each processing unit of this system is provided with a single wafer transfer unit for taking a semiconductor wafer at a time out of the mounted cassette to transfer the wafer to each processing portion. Therefore, since the number of processing units increases as the scale of the system increases, there is a problem in that it is required to increase the number of single wafer transfer units. In addition, since the kind of the processing unit varies in accordance with the kind of processing when the multi-product small-scale production is carried out, it is required to feed, e.g., a cassette capable of housing therein twenty five wafers, to each processing unit even if the number of semiconductor wafers to be processed is one or two. Thus, it is required to provide a large number of cassettes, so that there is a problem in that the size of a stocker for housing therein the cassette must be large.
Therefore, it has been studied that a buffer cassette having a large number of shelves for supporting thereon semiconductor wafers, and a single wafer transfer unit are mounted on an automatic guided vehicle to sequentially feed the semiconductor wafers into the buffer cassette from a cassette, which is mounted on a station of a stocker, by means of the single wafer transfer unit to carry the buffer cassette to a target processing unit to transfer the semiconductor wafers directly to the processing unit.
In such a system, the buffer cassette for housing therein the semiconductor wafers is fixed to the automatic guided vehicle. However, with respect to the size (diameter) of semiconductor wafers, 12-inch wafers capable of increasing the number of products have been provided in addition to conventional 8-inch wafers. Cassettes for housing therein only 8-inch semiconductor wafers and cassettes for housing therein only 12-inch semiconductor wafers have been produced on the basis of the SEMI standard. There are some cases where a factory includes a processing line for 8-inch wafers, a processing line for 12-inch wafers, and a processing line for 8-inch and 12-inch wafers. Although conventional processing lines are processing lines only for 8-inch wafers, there is some possibility that the layout of the processing line may be changed to that of a parallel line for 8-inch and 12-inch wafers or a processing line only for 12-inch wafers.
Therefore, there is a problem in that an automatic guided vehicle only for 8-inch wafers and an automatic guided vehicle only for 12-inch wafers can not be applied to a processing line including 8-inch and 12-inch wafers, and can not cope with the variation in size of wafers in accordance with the change of layout.
In addition, since the single wafer transfer unit is designed to pick a wafer up to transfer the wafer, the robot hand portion of the single wafer transfer unit is movable in vertical directions with respect to the vehicular body. Therefore, the robot hand portion is designed to move in vertical directions with respect to the ceiling plate of the automatic guided vehicular body.
The ceiling plate has an opening for allowing the passage of the robot hand portion in vertical directions, and a gap is formed between the ceiling plate and the single wafer transfer unit for vertically moving the robot hand portion with respect to the ceiling plate. When the robot hand portion moves downwards, air is discharged upwards from the gap. At this time, dust produced in the lift driving portion of the robot hand arranged in the automatic guided vehicular body is raised, so that there is a problem in that the raised dust adheres to the wafer supported on the robot hand.
In order to prevent the adhesion of dust, it is considered that a retractable protective cover, e.g., a bellow-like protective cover, is provided between the ceiling plate and the robot hand portion to cover the gap regardless of the vertical movement of the robot hand portion. However, with this construction, the protective cover causes dust.